1. Field of the Invention
The present invention relates to a numerical control apparatus for controlling machine tools and the like.
2. Description of the Prior Art
A numerical control apparatus primarily consists of a numerical control part, a motor control part, a motor amplifier, an amplifier power supply, and a motor. The numerical control part outputs a move command to the motor control part. The motor control part generates, based on the command, a PWM (Pulse Width Modulation) signal for rotating the motor by performing loop control processing of position and speed, and the like. The motor amplifier rotates the motor based on this PWM signal. The amplifier power supply provides the motor amplifier with driving power.
FIG. 2 is a schematic diagram of a conventional numerical control apparatus which has been commonly used. The numerical control part 1 is placed away from the power panel 3 along with the display 2. The power panel 3 is placed near the motors 6-1 to 6-4 which drive a machine such as a machining tool. And, on this power panel 3, there are placed motor amplifiers 5-1 to 5-4 for the respective motors which drive each moving part of the machine and an amplifier power supply 7. From this amplifier power supply 7, driving power is delivered to motor amplifiers 5-1 to 5-4 through a power line 9. The motor amplifiers 5-1 to 5-4 include motor control parts 41-1 to 41-4, respectively. Each of these motor control parts 41-1 to 41-4 is connected with the numerical control part 1 by a high-speed communication path 11 consisting of an optical cable or the like, and the numerical control part 1 and the motor control parts 41-1 to 41-4 exchange move commands and various signals with each other through a high-speed serial communication.
Move commands from the numerical control part 1 to the motors 6-1 to 6-4 are sent to the motor control parts 41-1 to 41-4 through the high-speed communication path 11. Upon receiving the move commands, the motor control parts 41-1 to 41-4 generate PWM signals by performing a loop control processing of position, velocity and current, and control the driving of motors 6-1 to 6-4 by controlling the motor amplifiers 5-1 to 5-4 based on the PWM signal.
FIG. 3 shows the numerical control apparatus disclosed in the Japanese Patent Application Laid-Open No. 09-69004; this numerical control apparatus consists of a digital signal processor (DSP) and others, in which a motor control part 42 for controlling a plurality of motors is provided in the numerical control part 1. The motor control part 42, and motor amplifiers 5-1 to 5-4 placed in the power panel 3 are connected by a high-speed communication path 13 of a daisy chain mode with a serial servo bus consisting of a optical fiber cable. Other configurations are the same as the prior art example shown in FIG. 2; the same elements as those of FIG. 2 are given like numerals.
In the prior art example shown in FIG. 3, the motor control part 42 performs loop control processing of position, speed and current for motors 6-1 to 6-4 based on the move commands given to the motors 6-1 to 6-4 from the numerical control part 1 to generate PWM signals so that the PWM signals are sent to the motor amplifiers 5-1 to 5-4 through the high-speed communication path 13. The motor amplifiers 5-1 to 5-4 control the driving of the motors 6-1 to 6-4 respectively based on the PWM signals.
In the numerical control apparatus shown in FIG. 3, since multiple motors 6-1 to 6-4 are controlled by a single motor control part 42, it is easy to perform a cooperative control of the motors. On the other hand, since the motor control part 42 is provided inside the numerical control part 1, a problem exists in that when the numerical control part 1 falls into an abnormal condition, this would affect the motor control part 42 as well thereby resulting in a complete failure of the control.
Also, in the numerical control apparatus shown in FIG. 2, the motor control parts 41-1 to 41-4 are separated from one another, and are provided along with motor amplifiers 5-1 to 5-4 for the motors 6-1 to 6-4. The apparatus offers an advantage in that even if the numerical control part 1 falls into an abnormal condition, the motors 6-1 to 6-4 can maintain a minimum level of control; however, it also has a drawback in that a cooperative control of the motors is difficult since the motor control parts 41-1 to 41-4 are distributed.
Moreover, in the prior art numerical control apparatus shown in FIGS. 2 and 3, since the numerical control part 1 and the motor amplifiers 5-1 to 5-4 are connected by means of optical fiber cables 11, 13, expensive optical interfaces must be provided for the motor amplifiers 5-1 to 5-4 thus resulting in a problem of high cost of the numerical control apparatus.